Telephone system



R. F. STEHLIK TELEPHONE SYSTEM Filed Nov. 22, 1 2 Sheets-Sheet N EN Iru rEmEr- Bu 5011311 F- EZEHIR June 12, 1928 June 12. 1928. v 1,673,212

R. F. STEHLIK TELEPHONE SYSTEM 'Filed Nov. 22. 1921 2 Sheets-Sheet 2 Patented June 12, 1928 UNITED STATES PATENT oFF1cE..

RUDOLPH F. STEHLIK, OF CHICAGO, ILLINOIS, ASSIG-NOR, BY MESNE ASSIGNMENTS,

TO AUTOMATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

TELEPHONE SYSTEM.

Application filed November 22, 1921. Serial No. 517,078.

The present invention relates in general to telephone systems, but is concerned more particularly with automatic telephone systems; and the object, briefly stated, is the.

potential upon it switches through in the usual manner but for some reason, due either to the line conductors or the release trunk conductor not being continuous or to the failure of the switch ahead to place ground upon the release trunk conductor, no holding circuit is established for the switching relay of the switch. \Vhen this occurs, the said switching relay deenergizes with the final result that the calling subscriber fails to get his number. This difficulty is overcome in the present invention in a manner which will be described fully hereinafter.

Referring now to the drawings which comprise Figs. 1 and 2, when they are, arranged in order with the corresponding lines of the end thereof in alignment they rep-resent by means of the usual circuit diagrams a sufficient amount of the apparatus in a system embodying the principlesof the invention to enable the same to be understood, Fig. 1, shows a substation A together with an individual line switch C and one of the selector switches to which this line switch has access. Fig. 2, shows .anautomatic repeater which may be seized by the selector shown in Fig. 1 and which is associated with the trunk line extending to a selector switch in the distant vofiice.

The substation A is an ordinary automatic substation having the usual talking, signalling, and impulse transmitting devices.

The line switch C is mechanically of the well known rotary type in which the wipers have no normal position and more in a for ward direction only. The circuits of this switch are shown complete and will be described full-y hereinafter.

The selectors D and F are mechanically of the well known vertical and rotary .type and accordingly have the r bank contacts arranged in horizontal rows or levels. The circuits of these switches also are shown-complete and will be described fully hereinafter.

I The automatic repeater E is'used prishowing the slugs on relays such as 15 on the top end of the coil, and the slugs on relays such as 16 on the bottom end of the coil.

The apparatus, having been described more or less in general, will'now be described in connection with a detailed description ofits operation. For this purpose it will be assumed that the'subscriber at substation A desires to make a call. When the receiver is removed at substation A, a circuit is closed over the line conductors 11 and 12 for line relay 15 of the line switch C. Line relay 15, upon energizing, prepares a circuit for relay 16 at armature 26; closes a circuit for switching relay 14; and stepping magnet 17 in series with armature 27 and at armature 24 connects the test wiper 31 to a point between switching relay 14 and stepping magnet 17. The operation now depends upon whether the trunk line upon which the wipers of the line switch are standing is busy or idle. If it is busy there is a ground potential upon the test contact thereof; switching relay 14 is short circuited and stepping magnet 17, which interrupts its own circuit, is operated in the manner of a buzzer to advance the wipers step by step in search of an idle trunk line. Assuming that the trunk line comprising conductors 36, 37, and 38 and terininating in bank contacts, 33,. 34;, and 35 is the first one found to be idle, switching relay 14 is no longer short circuited when the test wiper 3 1 arrives upon test contact 34 and accordingly energizes in series with steppin magnet 17, the said magnet 17 not energizing on account of the high resistance of switching relay 14. Switching relay 14, upon energizing, completes the circuit of slow acting relay 16 at armature 21. Relay 16, upon energizing, prepares acircuit for stepping magnet 17 at armature 28. As a further result of the energization of switching relay 14, it disconnects test wiper- 31 from the point between its own windlng and that of stepping magnet 17 and connects it to the grounded private normal conductor 13 at armature 22; and disconnects the line conductors 11 and12- from the winding of line relay l and ground, respectively, and extendsthem by way of armatur'es and 23 and their working contacts, wipers and '32, bank contacts 33 and 35, conductors 36 and 38, and armatures 72 and'75 and their resting contacts to the upper and lower windings, respectively, of the double wound line relay of the selector D. Line relay 45, upon energizing over the calling subscribers loop, closes a circuit for the release relay 46 including the resting contact of armature 74 and said armature,

at armature 55. Release relay46, upon energizing, opens axpoint in the circuit of re lease magnet and prepares a circuit for vertical magnet at armature 58;prepares a circuit for stepping relay 48 at armature 57 and at armature 56 places ground upon release trunk conductor-Why way of the normally closed contacts controlled by armature 61, thereby establishing the usual holding circuit for switching relay 14 of the lay 15 has had'time todeenergize.

line switch C beforethe slow acting linerel Vhen line relaylo falls back, it disconnects the grounded 'armature" 27 from the private normal conductor 13, butthe said conductor ismaintained grounded by release trunk conductor 37, as previously pointed out. As a fu'rtheriresult of the deenergization of line relay 15, it opens another point in the test circuit at armature24; closes still another pointin the circuit of stepping magnet 17 at armature 25; and at armature 26 opens the circuit of relay 16. r

In the'normal course of events, slow act ing relay l6 finally deenergizes and armature 28 opens thepoint previously closed in the circuit of stepping magnet 17. However, if we assume that the previously pointedout holding circuit is not'established, switching relay 14 ofthe line switch C deenergizes as soon as'the armature of line relay 15 falls back, thereby completing the following circuit for stepping-magnet 17: From ground by way-ofarmature 21 and its resting'contact, armature 25 and itsresting contact, armature 28 and its working contact, and stepping magnet 17 to battery.

As a further result of the deenergization ofswitching relay 14, it connects up line relay 15 again at armatures 20 and 23. Accordinglyline relay 15 and stepping magnet 17 start to energize simultaneously. Line reother notch on the ratchet Wheel (not shown) which is rigidly secured to the associated wipers. Line relay 15, upon energizing, in addition to its other circuit changes, opens the circuit of stepping magnet 17, at armature 25, whereupon the said magnet 17 deenergizes, thereby rotating the associated wipers into engagement with the next trunk. The testing for an idle trunk now proceeds in the usual manner. Obviously if the next trunk found to be idle is also open, it will be rejected in the same. manner as the trunk extending to the selector D'was rejected, and the wipers will be rotated'again in search of still another idle trunk. idle trunk is found in which all three conductors are continuous. In the present case, however, we may assume that the conductors of the trunk line extending to the selector D are continuous as shown and that, following the energization of switching relay- 14, the selector D establishes a holding circuit as hereinbefore described.

With the assumption as noted, the calling subscriber may now operate his calling device for the first digit of the desired number, thereby producing a corresponding number of interruptions in the circuit ofv line relay 45 of the selector D. Each time line relay 45deenergizes, it completes a circuit for vertical magnet '65 by way of armature 55'and its resting contact, and armature .58 and its working contact- .By the operation of vertical magnet x65 the shaft wipers of This process continues until, an r the selector D are raised step by step until i the latter come to rest opposite the desired level of bank contacts. As soon as the- 01f normal contacts 69 have closed, which occurs upon the first upward step of the shaft, the following circuit is completed for stepping relay 48 from ground and by way of armature 57"and its. working contact, armature 50 and its resting contact, interrupter contacts 71 of stepping magnet 70, off normal contacts 69, and the lower winding of stepping relay 48 to battery. Relay 48, upon ener izing, completes a locking circuit for itself as follows: from ground by way of the resting contact of armature 74 and said armature, armature 67 and its Working contact, and thence by way of the previously traced circuit to battery through tacts 69 close, upon closing, place relay 47 in multiple with the release relay 46, and accordingly a circuit is closed for the saidrelay 47 each time line relay energizes following an interruption produced in its circuit. Relay 47 however, has-a copper slug on its armature end, is of relatively high inductance compared to the other relays, and moreover has a relatively stilf adjustment and these things combined prevent the said relay 47 from operating while the armature 55 is vibrating under the control of the calling subscribers sender. Immediately after the armature 55 comes to rest in an energized condition, at the end of the series of interruptions, change over relay 47 energizes in multiple with release relay 46; closes a locking circuit for itself and disconnects itself from the multiple with relay 46 at armature 64; places a multiple ground upon release trunk conductor 37 and disconnects the said conductor 37 from armature 56 of release relay 46 at armature 61; prepares a circuit for the upper winding of stepping relay 48 at armature 62; connects up test wiper 77 at armature 63; and at armature opens the initial circuit of the lower winding of stepping relay 48, and completes the circuit of rotary magnet 70. Rotary magnet 70, upon energizing, advances the wipers 76, 77, and 78 into engagement with the first set of banl; contacts in the level opposite in which they are raised, at the same time opening its interrupter contacts 71, whereupon stepping relay 48 deenergizes and opens the circuit of rotary magnet 70 at armature 66. Rotary magnet 70, upon deenergizing, closes its interrupter contacts 71 again. From this point the operation depends on whether the trunk line terminating in the first set of bank contacts is busy or idle. If it is busy, there is a ground potential upon the associated test contact and stepping relay 48 energizes again over the following circuit: From ground by way of the test contact with which test wiper 77 is in engagement, test wiper 77, armature 73 and its resting contact, armature 63 and its working contact, and thence by way of a previously traced circuit to battery through the lower winding of stepping relay 48. Stepping relay 48, upon energizing, closes its previously described locking circuit at armature 67 and at armature 66 completes the circuit of rotary magnet 70 again. Rotary magnet 70, upon energizing, advances the wipers into engagement with the next set of bani: contacts and again opens its interrupter contacts 71. This alternate operation of stepping relay 48 and rotary magnet 70 continues until an idle trunk is reached. lVhen an idle trunk is reached, which trunk will be assumed to be the one comprising conductors 82, 83, and 84, switching relay 49, being no longer short circuited, energizes over the following circuit: from ground by way of the working contact of armature 56. and said armature, switching relay 49, and thence by way of a previously traced circuit, to battery, through the lower, winding of stepping relay 48. Stepping relay 48, however, does not energize in series with switching relay 49, owing to its own relatively small number of turns andits comparatively stiff adjustment. Switching relay 49, upon energizing, removes ground from armatures and 67 at armature 74; disconnects testwiper 77 from the point between its own winding and that of stepping relay 48 and it connects it to ground by way of armature 56 and its working contact at armature 73, thereby making the seized trunk busy immediately; and at armatures 72 and 75 disconnects conductors 36 and 38 from the windings of line relay 45 and extends them by way of wipers 76 and 78, bank contacts 79 and 81, trunk conductors 82 and 84, upper and lower left handwindings of the repeating coil associated with the repeater E to the upper andlower windings of line relay 101 of the repeater E. Line relay 101, upon energizing, closes a circuit for release relay 102 at arn'iature 110. Release relay 102, upon energizing, places ground upon release trunk conductor 83 at armature 112, thereby closing the usual holding circuit for switching relay 49 of the selector D before the slow acting release relay 46 of the said selector has had time to deenergize. Release relay 46,upon deener gizing, opens the initial energizing circuit of switching relay 49 at armature 56, but the said switching relay 49 is maintained energized over the previously described holding circuit. As a further result of the deenergization of release relay 46, it prepares a circuit for release'magnet at armature 58, and at armature 57 closes a circuit for the upper winding of stepping relay 48 by way of armature 62 and its working contact. Stepping relay 48, upon energizing, prepares a circuit for rotary magnet at armature 66 and at armature 67 prepares a locking circuit for itself. Eventually, however, slow acting relay47 deenergizes; opens the circuit ofstepping relay 48 at armature 62; and at armature 61 disconnects release trunk conductor 37 from direct ground, and connects it to ground by way of the holding circuit coming back from the repeater E.

If. we assume now that one of the three conductors of the seized trunk is open when the trunk is connectedwith as described, or that for any reason the repeater E fails to place ground upon conductor 83, there is no holding circuit completed for switching relay 49 and accordingly the. de-' and also by the energization of stepping re- ].ay 48 as mentioned hereinbefore. Upon deenergizing, switching relay 49 completes a locking circuit for stepping relay 48 at armature 74 and connects up line relay again at armatures 72 and 75. It will be noted that as a result of the deenergization of switching relay 49 there is a circuit closed, including armatures 74, 55, and 58 and off normal contacts 59, for release mag net 60. Release magnet 60, however, is not able to attract its comparatively heavy armature before its circuit is opened at armature 55, ,upon the energization of line relay 45. As a further result of the energizationof line relay 45, it closes the circuit of release relay 46. Release relay 46, upon energizing,

bank contacts and o ens its interru ter con-.

tacts 71, whereupon stepping relay 48 deenergizes and opens the circuit of rotary magnet at armature 66. Rotary magnet 70, upon-.deenergizing, closes its interrupter contacts 71 again. f the trunk line terminating in this set of contacts is busy, the

rotary movement continues in the usual manner unt1l an idle trimkhne 1S reached,

whereupon s'wltching relay 49 energizes 1n the usual manner and extends the connec tion through to the switch ahead. Obviously it this trunk line also is open, it is rejected in the same manner as the one com prising conductors 8284, inclusive, was rejected and the wipers are rotated into engagement with the next idle trunk. This operation continues until an idle trunk is found in which the conductors are continuous.

In the present case, however, we shall assume that the conductors of the trunk line extending to the repeater E are continuous shown. lVith the assumption as noted, the wipers of the selector D remain in en gagement with the contacts 7981, inclusive. In the. repeater E, as a further result of the energization of line relay 101, a bridge is completed across the conductors 113 and 114leading to the selector Fin the distant oiiice. In response to theclosure of this bridge, line relay. 125 of the selector F energizes and completes a circuit for release.

, relay 126 and change over relay'127 in multiple at armature 135- Release relay 126, upon energizing, opens a point in the second digit of the desired number, thereby producing a corresponding number of in terruptions in the circuit of line relay 101 of repeater Each time line-relay 101 deenergizes inresponse to one of these interruptions it opens the circuit of line relay 1250f selector F. Each time line relay 125 deenergizes, it closes the circuit of vertical magnet 142 by way of armature 138 and its working contact. By the operation of vertical magnet 142-, the shaft and wipers of the selector F are raised step by step until the latter stand opposite the desired level of banlrcontacts, which we shall assume is the level in which the trunk line comprising conductors 157-159, inclusive, terminates. Relay 127' deenergizes in responseto the opening of its circuit at armature 185 as soon as the line relay 125 responds to the first interruption, and being of relativelyhigh inductance compared to the other relays and stiflly adjusted does not energize again until armature 1555 comes to rest at the end ofthe series of'interruptions. As soon as the off normal contacts 143 close, stepping relay 128 energizes over the follow ing circuit: from ground, by way of the resting contact of armature 149 and said armature, armature 130 of change over relay 127 and its resting contact, working contact of armature 137 and said armature, interrupter contacts of rotary magnet 146, off

normal contacts 143, and stepping relay 128 to battery. Stepping relay 128, upon energizing, closes a locking circuit for itself at armature 145 and at armature 144 prepares a circuit for rotary magnet 146. When change over relay 127 energizes again at the end of the vertical movement, it opens the initial circuit of stepping relay 128 and closes the circuit of rotary magnet 146 at armature 130, and at armature 141 con nects up test wiper 152. Rotary magnet 146, upon energizing, rotates the wipers 151-153, inclusive, into engagement with the first set of contacts in the level opposite in, which they are raised and opens the cir-- cuit, of stepping relay 128. Stepping relay 128, upon deenergizing, opens the circuit of rotary magnet 146 at armature 144, whereupon the said rotary magnet 146 deenergizes also and again closes its interrupter contacts. From this point the operation depends upon whether the trunk line terminating in the first set of contacts is busy'or idle. If itis any useful function at this busy, stepping relay 128 energizes again in the usual manner, and rotary magnet 146 rotates the wipers into engagement with the next set of bank contacts. This operation continues in the usual manner until an idle trunk line is found. When an idle trunk line is found. which trunk will be assumed to be the trunk comprising conductors 157159, inclusive, switching relay 129, being no longer short circuited, energizes in series with stepping relay 128; removes ground from armatures 135 and 130 at armature 149; opens the test circuit and prepares the holding circuit at armature 148; and disconnects t-runk conductors 113 and 114 from the upper and lower windings of line relay 125 and extends them by way of armatures 147 and 150 and their working contacts, wipers 151 and 153, bank contacts 154 and 156, and trunk conductors 157 and 159, to the upper and lower windings of the line relay of the switch (not shown) to which the trunk line extends. The line and re lease relays of the said switch now energize in the usual manner and the latter places ground upon release trunk conductor 158, thereby establishing the usual holding circuit for the switching relay of selector F.

In .the selector F, relay 127, upon deenergizing, in response to-the opening of its circuit at armature 149 of switching relay 129, opens still another point in the. test circuit, so as to maintain the said test circuit open while the wipers are being restored to normal position, which occurs subsequently. Release relay 126, upon deenergizing. opens the initial circuit of switching relay 129 at armature 136, but the said switching relay 129 is maintained energized through the previously described holding circuit.

Assuming now that the previously mentioned holding circuit for switching relay 129 is not established, the deenergization of release relay 126 is followed by the deenergization of switching relay 129. Switching relay 129, upon deenergizing, connects up line relay 125 again at armatures 147 and 150 and at armature 149 closes a circuit for release magnet 140, including armatures 135 and 138, and 011' normal contacts 139. This circuit, however, is opened by line relay 125 before the said release magnet 140 has had time to energize. As a further .result of the energizat-ion of line relay 125, it closes the circuit for release relay 126 and change over relay 127 in multiple. Change over relay 127, however, as before stated, is constructed and adjusted, so as to be comparatively slow in energizing and consequently its armature remains inert for an interval. Release relay 126, upon energizing, prepares a circuit for switching relay 129 at armature 136, and atarmature 137 completes the following circuit for stepping relay 128: From ground by wayof the resting contact of armature 149 and said armature, armature 130 and its resting contact, working contact of armature 137 and said armature, and thence by way of a previously, traced circuit to battery, by way of-stepping relay 128. Steppin relay. 128, upon energizing, completes a locking circuit for itself at armature 145, andat armature 144 prepares a circuit for rotary magnet 146. Change over relay 127, upon energizing, connects up test wiper 152 at armature 141, and closes. the circuit of rotary magnet 146 at armature 130. Rotary magnet 146, upon energizing, advances the wipers into engagement with the next set of bank contacts and opens the circuit ofstepping relay .128. Stepping relay 128, upon deenergizing, opens the circuit or rotary magnet 146 atarmature 144. Rotary magnet 146, upon deenergizing, closes its interrupter contacts again, This alternate operation of stepping relay 128 and rotary magnet 146 continues in the usual manner until another idle trunk line is found, whereupon switching relay 129 energizes in the usual manner and extends the connectionto the seized trunk. If this trunk also is open, the same process is repeated with the result that anothertrunk is selected. This continues until an idle trunk is found that has continuous.

After a trunk is found that has the three conductors continuous, the calling subscriber may manipulate his calling device in accordance with the remaining digits of the desired number, whereupon the connection is extended to the desired line in the usual manner, After the connection is finally completed, the calling and called subscribers may converse with each other as desired, as much of the talking circuits as are shown being outlined by the heavy conductors.

When the conversation is completed, the calling'and called subscribers replace their receivers. When the receiver is replaced at the substation A, the circuit of line relay 101 of the repeater E is opened. Line relay 1.01, upon deenergizing, opens the connection extending ahead at armature 111 and at armature 110opens the circuit of release relay 102. Release relay 102, upon deenergizing, removes ground'from release trunk conductor 83 at armature 112, whereupon switching relay 49 of the selector D and switching relay 14 of the line switch C deenergizes. The deenergization of switching relay 14 restores conditions in the line switch C to normal. In the selectorD, switching relay 49, upon deenergizing,completes the following circuit for release magnet 60: from ground by way of the resting contact ofarmature 74 and said armature, armature 55 and its resting conthe three conductors tact, armature 58 and'its resting contact, off normal contacts 59, and release magnet 60 to battery. By. theoperation of release magnet 60, the shaft and wipers of the selector D are restored to normal position inthe usual manner, the circuit of release magnet 60 being opened at oft normal contacts 59 by the switch shaft when it reaches normal position@ In regard to therconnection beyond the repeater E, it may be said that when the-bridge across conductors 113 and 114 is opened at armature 111 of line relay 101, the line release relaysof the final switch deenergize and the latter removes ground from release'trunk conductor 158, thereby opening the circuit of the switching relay 129 of the selector F. Relay 129, upon deenergizing, closes the circuit of releasemagnet 140 at armature 149. By the operation of the said release magnet, the shaft and wipers of the selector F are restored-to normal position in the usual manner. The entire connection is now released and the apparatus is ready for another call.

.. It will be noted, upon a cursory examination of the drawings, that the circuits of the selectors D and F, while in many respects very similar, differ somewhat. in detail. This diflerence is due to the fact that the selector F is an incoming selector and has no release trunk conductor extending back from it, while the selectorv D must keep ground upon the associated release trunk conduetor so as to hold up the switching relay of the line switch until a trunkhas' been selected and a-holding circuit has been established from the switch ahead. ,TlllS makes it necessary to provide some means for holding the release trunk conductor 37 grounded inde endent of release relay 46 momentarily a ter the connection has been cut through and until the trunkhas been tested for continuity. This is accomplished, as before pointed out and explained, by making the change over relay 47 slow to release in addition to being slow to'pull up; No such precaution is necessary, however, in the selector I for the reason that it has no release trunk conductor associated with it.

The various features of the invention, hav ing been described and ascertained, will now be pointed out in the'appended claims.

hat is claimedis:. V r

1. In a telephone system, a subscribers line switch, subscriber controlled means for causing said'switch to select an idle one of a plurality of trun'ks,a line relay, means responsive to the energization of said line relay for initiating the trunk selecting operation, a switching relay and means for energizing ittm connect the subscribers line with the selected trunk at the end of the trunk selecting operation, and means for denext trunk in case one ofthe conductors of the selected trunk is open. 7

2. In a telephone system, a subscribers line switch having no normal position, subscriber controlled means for causing said switch to select an idle one ofa plurality of trunks, a line relay for initiating the trunk selecting operation, a switching relay and means for energizing it to connect the line with the selected trunk at the 'end of the trunk selecting operation, and means for deenergizing said switching relay and for reinitiating the trunkseleeting movement in case one of the conductors of the selected trunk is open.

3. Ina telephone system, a subscribers' individual line switch operable to select and stop on the first idle one of a plurality of trunks, and means operated automatically whenever one of the talking conductors of the selected trunk is open for causing the switch to always select the next idle trunk.

4. In a telephone system, an automatic switch of the non-restoring type having one or more talking conductors, a plurality of trunks accessible to said switch, each of said trunks comprising one or more talking conductors, means responsive to the initiation of a call for starting said switch from, its last operated position to select an idle trunk, means for stopping the trunk selecting operation when an idle trunk is reached, means responsive thereto for'connecting' the talking conductors of said switch with the talking conductors of said idletrunk, and means operable thereafter in caseone of the conductors of said idle trunk is openior causing the said switch to select another idle trunk.

5. In. a telephone system, a switch having a primary movement and a secondary trunk hunting movement, a relay deenergized during the primary movement, means for starting the secondary movement by. energizing said relay, means for stopping the secondary movement and for deenergizing the said relay when an idle trunk is found, and means operablewhenever the idle trunk is open or ceiver at a station of said line to automatically select and stop in engagement with an idle one-oi said trunk lines, and means automatically operative for causing said switch to continuethe trunk selecting operation at the next successive trunk should a conductor of the firstselected trunk be open.

7. In a telephone system, a subscribers line, a trunk hunting switch, means in said switch responsive to the initiation of a call for causing said switch to automatically select an idle one 'ofa plurality of trunks,

Hill

a relay for initiating the trunk selecting operation, another relay including means for causing it to operate to connect the subscribers line with the selected trunk, means for deenergizing said last relay and for reinitiating the trunk selecting operation should one of the conductors of the first selected trunk be open, and a circuit controlled by said last relay for reinitiating said selecting operation as set forth.

8. In a telephone system, a switch automatically operable upon the initiation of a call to select and stop on the first idle one of a plurality of trunks, and means automatically operated whenever one of the talking conductors of the selected trunk is open for causing said switch to select the next succeeding idle trunk.

9. In a telephone system, a subscribers individual line switch having a relay the coil of which is normally in the line circuit, a relay arranged to break the circuit of said first mentioned relay, and a slow to release relay, a motor magnet for rotating said switch, and an operating circuit directly controlled by all of said relays jointly for operating said magnet.

10. In a telephone system, a subscribers individual line switch having a line relay, a switching relay, and a slow to release relay, an operating circuit for said slow to release relay controlled by said other relays jointly, a motor magnet for rotating said switch, and an operating circuit controlled by all of said relays jointly for operating said magnet.

11. In combination, a switch including trunk selecting wipers, a plurality of trunks accessible thereto, said wipers normally resting on the trunk last used, means responsive to' the initiation of a call for seizing the trunk associated with the wipers, means for indicating a normal condition of the seized trunk, and means responsive to the failure of the indication for selecting a different trunk.

12. In combination, a nonnumerical switch including trunk selecting means, a plurality of trunks accessible thereto, means responsive to the initiation of a call for selecting an idle trunk, means for seizing the selected trunk, means for indicating a normal condition of the seized trunk. and means responsive to the failure of the indicationfor selecting a different trunk.

13. In a trunk selecting switch, trunk selecting wipers resting on the contacts last used. means responsive to the initiation of a call for causing the wipers to move from trunk to trunk, means for causing the wipers to temporarily stop and seize an idle trunk, means in the last trunk for indicating a normal condition of said trunk, and means responsive to that indication for preventing the continued movement of said wipers.

14. In a telephone system, a nonnumerical trunk selecting switch, means responsive to the initiation of a call for seizing an idle trunk, means in said trunk operated responsive to its seizure to indicate a normal condition of said trunk, and means in said switch operated upon the failure of the indication to cause the release of the trunk and the selection and seizure of a different. trunk.

15. In a trunk selecting switch, trunk selecting means, a sl0w-to-release relay energized responsive to the initiation of a call, means responsive to the operation of said relay to cause said means to select an idle trunk, a second slow-to-release relay, a quick acting relay operated responsive to the selection of an idle trunk to seize said trunk, to break the circuit of said first named relay, and to establish a circuit for said second slow-acting relay, and circuit connections to said trunk selecting means including contacts on the third relay established in case said third mentioned relay releases before the second mentioned relay releases. I

16. In a trunk selecting switch, three relays, a stepping magnet, an operating circuit for said magnet, said circuit having two branches, one of said branches extending through a front. contact on the first of said relays, and the second branch extending through a front contact on the second of said relays and a back contact on each of the remaining two relays.

17. In a trunk selecting switch, three relays, trunk selecting means, an operating circuit for said means, said circuit having two branches, one of said branches extending through a front contact on the first of said relays, and the second branch extending through a slow-to-open front contact on the second of said relays and a back contact on each of the remaining two relays, an operating circuit of said first relay extending through a calling line and through back contacts controlled by the third relay, an operating circuit for said second relay extending through front contacts on the third relay, an operating circuit for said 'third relay extending througha front contact of said first relay, a circuit established when the selected trunk is busy to prevent the operation of said third relay, a holding circuit for itself established by said third relay if the selected trunk is normal, whereby if said holding circuit is not established the third relay returns to normal and establishes the operating circuit to the trunk selecting means through said second branch.

18. In a trunk selector having primary and secondary movements, means for moving the selector in its two movements, a slow-acting relay front contacts of which control the primary movement of the selector, means for seizing an idle trunk, a second slow-acting relay maintained operated during the secondary movement of the selecnamed relay and the means for moving the tor and released-upon the seizure of a trunk, switch in its secondary movement. 7 I e a circuit established under predetermined In Witness whereof, I hereuntosubscribe 10 conditions after said second named relay is my name this 15th day of November; A. 1).,

5 released but before it operates to cause the 1921,

trunk selector to select a different trunk, said circnit including contacts on said second RUDOLPH F. STEHLIK. 

